Synthesis of N(SiMe3)2 supported vanadium(III) complexes, including hydrocarbyl, tetrahydroborate and azaalkenylidene derivatives†

Abstract

Reaction of [(Me₃Si)₂N]₂VCl(THF) (THF = tetrahydrofuran) with MgMe₂ or LiMe afforded [(Me₃Si)₂N]₂VMe(THF) in 70% yield. Nitrogen donors displaced THF in these V^III species, and [(Me₃Si)₂N]₂VCl(lut) (lut = 3,5-dimethylpyridine) and [(Me₃Si)₂N]₂VMe(pyr) (pyr = pyridine) were isolated and characterized. Solution thermolysis of [(Me₃Si)₂N]₂VMe(THF) yielded the known V^III dimer {[(Me₃Si)₂N]V(µ-CH₂SiMe₂NSiMe₃)}₂ in 73% yield. Reaction of [(Me₃Si)₂N]₂VMe(THF) with 3 equivalents of RNC (R = Bu^t or Xyl; Xyl = 2,6-dimethylphenyl) gave diazavanadacycles of empirical formulae [(Me₃Si)₂N]₂V[(Me)(CNR)₃]. For R = Bu^t, the product [(Me₃Si)₂N]₂V[Bu^tNCMeC(CNBu^t)NBu^t] features an exocyclic keteneamine functionality; for R = Xyl, an additional C–C bond forming step results in slightly more complex connectivity, to give [(Me₃Si)₂N]₂V[N(Xyl)CMeC–C(NXyl)CMeCHCH–CHCMeC(N)]. The crystal structures of both compounds are presented. Alkylation of [(Me₃Si)₂N]₂VCl(THF) with 2-thienyllithium led to isolation of [(Me₃Si)₂N]₂V(2-C₄H₃S)(THF) (60%). A blue solution that acted as a source of ‘[(Me₃Si)₂N]₂VPh’ was obtained from the reaction of 0.5 equivalent of MgPh₂ with [(Me₃Si)₂N]₂VCl(THF). The addition of pyr or PhCN to the blue mixture gave [(Me₃Si)₂N]₂VPh(pyr) (60%) and [(Me₃Si)₂N]₂V(NCPh₂)(NCPh) (66%), respectively. The chelated aryl amine [(Me₃Si)₂N]₂V(o-Me₂NCH₂C₆H₄) was synthesized from [(Me₃Si)₂N]₂VCl(THF) and Li(o-Me₂NCH₂C₆H₄) in 81% yield. Treatment of [(Me₃Si)₂N]₂VCl(THF) with excess LiBH₄ in the presence of pyr afforded the vanadium tetrahydroborate [(Me₃Si)₂N]₂V(η²-BH₄)(THF) in 41% yield. The solid-state structures of [(Me₃Si)₂N]₂VPh(pyr), [(Me₃Si)₂N]₂V(NCPh₂)(NCPh), [(Me₃Si)₂N]₂V(η²-o-Me₂NCH₂C₆H₄) and [(Me₃Si)₂N]₂V(η²-BH₄)(pyr) are reported.